Composite signaling system



Feb. 26, 19.35. J. B. M KI M COMPOSITE'SIGINALING SYSTEM Filed July" 26," 1953 Alli.

W air .26 quit $6 KN 5 MN INVENTOR J 8. Mc KIM 'BY A TTORNEV Patented Feb. 26,193fi COMPOS E N. Y., assignor to Bell Telephone Laboratories, Incorporated, NewYork, N.'Y.;a corporation of New York Appli cati on July 26, 1933, Serial No; 682,195

6 Claims. (01. 179-4) This invention relatesto signaling systems and more particularly to-duplex, composite telephone and telegraph systems. l g Y An object of the invention is to extendthesig- 5 naling range of such systems. over relatively high 'resistanceyline conductors without the use of supersensitive or critical electromagnetic devices. A feature of theinvention whereby the foregoing object is attained resides in the substitu .tionof gas-filled discharge devices for'the polarized electromagnetic relays previously employed insuch systems, said discharge devices operating on line potential variations transmitted over the line. These discharge devices are connectedgto the line and the respective terminal sourcesof signaling potentialbymeans of 'aproperly arranged resistance network whereby any variation of the line potential occasioned by a change in eitherterminal source, as for example,by a reversal of polarity, will cause a change only in the potential of the control electrodeof the distant discharge device in such'a direction as to cause itto start discharging, the discharge device at the nearend of the line remaining inert.

1 Stillanother feature; resides in an arrangement comprising a thermionic tube associated with the control electrode of the discharge device and controlled over a pilot channel adjacent to and subject tothe same earth potential as thegsignal channel whereby an equalizing bias is applied to the control electrodeof the discharge device to compensate for the voltage changes in the signaling line due to said earth potential. 1 a g j 1 A complete understanding of the operation the system contemplated by the invention as well as an appreciation of its various featuresmay be gainedfrom a consideration of the following 'detailed description and the annexed drawing.

Referring now to the drawing, there is shown a two-way composite trunk system extendingbetween two stations, Aand B. The trunk termi-.

nates atoffice A in jack 3and at oflice B in jack 4.

The alternating current telephone signals are transmitted between the stations over conductors 1 and 2 in the usual mannencondensers 5 and 6 at ofiice A and 7 and 8 at ofiice B presenting a low impedance path for these signals. l

For the initiation of the direct current signals to be transmitted over a composite leg ofthe system, relay 9jis provided at office A and relay 10 at oiiice B. Means forcontrolling theoperation of these relays are provided at each ofiice and, are indicated'schematically at 11 and 12, respectively. The direct current signals may be used for'telegraphy in which instance telegraph keys may be provided to. control the operation of relays 9 and 10;i' Again, it may be desirable to transmitadirect current signal for supervisory purposes during the setting up of the: telephone connection in which instance-the'control of relays9 andlOmay reside in other relays (locatedwithin the rectangles 11 and 12) operating, for example, over the sleeve circuits of the respective jacks 3 and 4.

Sources of negative potential, 21 and 13,1re- .spectively, are associated with the armature circuits of relays 9 and 10 asare also resistancenetworks comprising, atstation A, resistances 15, 16 and 17 and at station E, resistances 18, 19 and 20.

The direct current signal receiving set provided at station A includes a gas-filled discharge tube 23, a pair;of polarizedrelays 24 and 25 and a windings, an upper or operating winding and a lower or biasing winding; Current normally flows from battery 69 through the biasing winding of each relay in such'a direction that their armatures are normally held in a released condition.

.ample, beconstructed as described in Patent No. 1,921,004, issued Aug. 8, 1933, to A; L. Samuel.

lamp 26. Each of the relays is provided with two According to the characteristics of tubes of this type; for a given; plate voltage, a negative grid bias below a given voltage will preventthe passage of plate current. Upon a sufficient change .of the grid bias in a positive direction. however,

the plate circuit passes current,'ionization of the gas in the tube occurs, that is, the tube breaks down asit is commonly stated, and the grid loses control. The discharge inthe tube, once started, persists until the positive plate current is interrupted. l

s A vacuum tube 31 (not a trigger-tube isalso associated with the direct current signal receiving set for a purpose and operating in a manner to be subsequently described in detail.

. The directcurrent signalreceiving set at station B is similar to that of station A and includes trigger tube 27, polarized -relaysl28v and 29,

lamp 30 Retardation coils and 75 are connected in the line at station A and retardation coils 36 and 76 are. connected in the line at station B, the windings thereof providing a low impedance path for and vacuum tubelnot a trigger tube) direct current signals received over conductors 45, i

.46, 47 or 48 and; at the same time, due to their inductance, preventingpassage of the alternating current telephone signals into the direct current signal sending and receiving portions of the system. A lowimpedancepath to ground is provided through condensers 37,38, 39, 40, 41, ,42, 43 and 44 for the small amount of, alternating currentthat may traverse the windings of the re tardation coils.

Let us now assumeffor purposes-of i1lustration, that, in order to transmitadirect current signalfrom station A to station B, the means .providedwithin the rectangle 11, for controlling relay 9, be operated.

to I

Normally, i. e. when relay 9 is in its unoperated position, a negative bias from battery 21 is applied to the grid of trigger tube 2'? of sumcient value to prevent the. tube from discharging. This negative bias is applied through a circuit traced from battery 21, upper break contact of relay 9, resistance 15, conductor 45, lower winding of 19 and 20 at station B of respective equal values are such with respect to each other and to the line resistance that any potential variation at either station will be effective to vary, in a positive direction, the potential applied to the grid of the trigger tube at the distant station only and will cause no change, in a positive direction, in the potential applied to the grid of the trigger tube a at the near or home station.

Assuming now that, due to operation of means included within rectangle 11, relay 9 be operated, the source of negative potential 21 is removed from line 2 and ground 22 is connected thereto. Upon removal of the negative potential 1 from the line, the potential of the grid of tube 2'7 becomes less negative by such an amount that the tube breaks down and discharges. No change in a positive direction occurs in the potential applied to the grid of tube 23 however due to the relative values of resistances 15, 16 and 17,

referred to above.-

As tube 27 breaks down and the space current path is set up current flows through the upper or operating windings of relays 28 and 29 in the proper direction to cause both relays to operate. The ratio of the resistances of the operating and biasing windings of the relays is such that the effect of the current normally flowing through the biasing windings is overcome by the current now passing through the operating windings and the relays operate. Operation of relay 29'comp1etes a circuit from battery 64, lamp 30, make contact of relay 29 to ground 65, lamp 30 being energized over this circuit and serving as an indication of the operation of relay 9 at station A.

Now as relay 28 operates it completes a path through lead 71 and the armature of relay 28 which acts to short circuit the upper or operating winding of relay 28 and the plate of discharge tube 27. Relay 29 is held operated over this path'while the discharge in tube 27 is interrupted, due to the short circuiting of the plate, and control of the tube is returned to the grid.

'As current in the upper winding of re1ay28 is interrupted the armature moves to its released position by virtue of the current flowing through the lower or biasing winding, thereby removing the short circuit from the plate of tube 27. I Assuming that, when thedischarge in tube 27-is interrupted and control of the tube returned to the grid, relay 9 is stilloperated, tube 27 immediately breaks down again and relay 28 again operates. This cycle is repeated at a rapid rate,

relay 28in effect buzzing and causing the discharge in tube 2'7 toalternately start and stop at the same rate. Relay 29 remains steadily operated during the buzzing action, of relay 28.

The intermittent operation of tube 27 and relay 28 continues until'relay 9 restores to normal whereupon, as the discharge in tube 27 is interrupted as above described, the grid of the'tube is held at a sufficiently negative bias by virtue of source of negative potential 21, now applied to the line, that the tube does not again break down as relay 28 releases. The armature of relay 29 thereupon moves to released position by virtue of the current through the lower or biasing winding and lamp 30 is extinguished.

It will be apparent from the above description that operation of relay 9 at station A causes energization of lamp30 at station B and that the lamp remains energized as long as relay 9 remains operated. Return of relay 9 to normal condition results, in turn, in the deenergization of lamp 30. If desirable a locking relay circuit may be inserted between the armature circuit of relay 29 andlamp 3O whereupon lamp 30 will remain energized after the-release of relay 29. The locking circuit may be anyof the ordinary and well known arrangements and has not been shown in the drawing. I

Lamp 26 at station A is, in a manner similarto that just described in connection with the energization of lamp 30 at station B, energized upon the operation of relay 10 at stationB and remains in energized condition until the relay returns to normal position.

In view of the fact that, as stated above, the ratio of the resistances of the network associated with each relay (15, 16 and 17 at station A and '18, 19 and 20 at station, B) is such that the position, operated or normal, of the. respective relays has no effect on the condition of the trigger tube at the same station, it will be apparent that the system provides two-way operation, i. e., signals may be sent from A to B without afiecting lamp 26 and from B to AWithout affecting lamp 30. The response of relay 29 to incoming signals is not affected by the condition of relay 10 in transmitting signals nor is the response of relay 25 affected by the condition of relay 9. r 1

In order to prevent variations in earth potential between the two ends of the line from afiecting the. operation of the'circuit, means have been provided at each station for equalizing the effects of such variations. A vacuum tube and associated circuit are provided at each station (31 at station A and 32 at station B) and are connected through respective leads 46 and 48 to conductor 1 which is adjacent to and subject to the same variations in earth potential as conductor 2.

9 Referring to station A, the output of vacuum tube 31 is affected by the same variation in earth potential appliedto the grid over conductor 46 as that which is applied to the grid of discharge tube 23 over conductor 45.

The

voltage drop across resistance 51 is applied to the grid of tube 23 through resistance 50. This potential varies as the output of tube 31 is varied by the variation in earth potential applied to the grid. The ratio of resistances 50, 51 and 52 is such that variations in earth potentialin line 1 will so vary the output of tube 31 and the potential applied thereby to the grid of tube 23 that the effect on the grid of tube 23 of the same variations in earthpotential in conductor 2, is neutralized. Y

Tube 32 and associated circuit at stationB act in a similarmanner to neutralize the efiect of variations 1 in earth potential on the gridof tube 27.

While one specific embodiment ofthe invention has been selected for. detailed description the invention is not limited in its application to such a system. The. invention. is intended to be limited only as claims.

What is claimed is: i

1. In a duplex signaling system, a line, a grounded source of potential at each end of the line, a resistance network connected inpare allel with each potential source, a connection between each end of the line and a point in its respective network, transmitting means at each end of the line for varying the potential of the line, a gas-filled discharge tube comprising a control electrode associated with each network, a connection between each control electrode and its associated network at another point therein, a signal receiving device controlled by each discharge tube, a pilot line adjacent to said signaling line and subject to the same earth potential, a thermionic device at each end of said pilot line and controlled thereover, and a connection including a high resistance between the output of each thermionic deviceand the controlelectrode of its respective discharge device whereby the control electrodes are subjected to an equalizing bias to compensate for potential variations in the signaling line due to earth potential.

2. In a direct current duplex signaling sysindicated by the attached tem, a line circuit, a resistance network at each end thereof, a space discharge device including a control electrode at each end of the line, a connection'between each control electrode and an intermediate point same end of the line, a connection between each end of the line and two other points in the network thereat, a source of direct. current connected in parallel with each network, said sources being so poled with respect to the network and said intermediate network points so chosen that a predetermined negative bias normally exists on said control electrodes, a signal receiver associated with each discharge device and controlled thereby, and transmitting means at each end of the line 'for varying the potential of the source thereat to decrease the negative bias on the control electrode of the distant end of the line and prevent any change in a positive direction on thenear electrode whereby the distant discharge device only is caused to operate its associated receiver. 1

3. In a direct current duplex signaling system, a lineconductor, a resistance network at each end thereof, a space discharge device including a control electrode at each end of the line, a connection between each control electrode and an intermediate point in the network at the same end of the line, a connection between each end of the line conductor and another intermediate point in the associated network, a grounded source of direct current connected in parallel with each network, said intermediate connections being so chosen and. said grounded sources sopoled that a predetermined negative bias normally exists on the control electrodes at both ends of the line, a signal receiver associated with each discharge device and controlled thereby, and transmitting means at each end of the line for varying the potential of the source thereat to decrease the negative bias on the control electrode at the distant end of the line and prevent any change in a positive direction on the near electrode whereby thedistant discharge device only is caused to operate its associated receiver.

in the network at the mined critical value, a connection between each end of theline conductor and the junction of the high and low resistances at that station, a connection between each control electrode and an intermediate point in the associated high resistance, a signal receiving device controlled by each discharge device, said current sources being so "poled with respect to the line and said control electrodes being connected at such points in the high resistances that normally both control electrodes are below the predetermined critical value at which the discharge device becomes active, and

transmitting means at each station for reversing the grounded source thereat with respect to the high resistance and line conductor to raise the potential of the control electrode at the distant station only above said critical value.

5. In a direct current duplex signaling system, two signaling stations, a source'of direct current at each station having their positive poles grounded, a high resistance and a relatively low resistance in shunt to each source, a receiving circuit including a gas-filled discharge tube at each station, a control electrode for each tube, a connection between each electrode and an intermediate point in its associated high resistance, said intermediate point being so chosen that the connected control electrode normally has a predetermined negative bias with respect to ground, a line cone ductor connected to junctions of the highand low resistances of each station, and transmitting means at each station for grounding the line conductor through the low resistance thereat to raise the potential of the control electrode at the distant station and thereby energize the receiving circuit. I l 6. In a direct current signaling system, a transmitting station and a receiving station, a grounded source of directcurrent at the receiving station, a shunt circuit connected across said source including a high resistance and a relatively low resistance, a line conductor extending between said stations and connected to the junction of the high and low resistances at the receiving station, a gasfilled discharge tube including a control electrode at the receiving station, a connection between the control electrode and an intermediate point in.

the high resistance, said point being so chosen and said source so poled with, respect to the shunt circuit that a predetermined negative potential bias with respect to ground normally exists on the control e1ectrode,a receiving device controlled by said discharge tube and adapted to be operated a when the control electrode potential is raised 6 above said normal bias, a resistance at the transmitting station equal to the low resistance at the receiving station, and means at the transmitting station for grounding said line conductor through the resistance thereat to raise the potential of the control electrode at the receiving station and operate the receiving device. l v a JAMES B. McKIM. 

